KR100385190B1 - Cold cathode fluorescent lamp driving device using piezoelectric transformer - Google Patents

Abstract

According to the present invention, the AC drive signal having the frequency near the resonance frequency of the piezoelectric transformer is generated by the variable oscillation circuit, the output signal waveform of the variable oscillation circuit is shaped substantially in the form of a sinusoidal wave by the waveform shaping circuit, Current amplification or voltage amplification is performed by the drive circuit so that the output of the piezoelectric transformer is amplified to a level sufficient to drive the piezoelectric transformer. In addition, when the output of the driving circuit is subjected to a current limitation and is input to the piezoelectric transformer, the output signal of the transformer is applied to the cold-cathode fluorescent lamp so as to light the cold-cathode fluorescent lamp and the impedance of the cold- Can not.

Description

Cold cathode fluorescent lamp driving device using piezoelectric transformer

The present invention relates to a cold cathode fluorescent lamp driving apparatus using a piezoelectric transformer for converting the magnitude of an AC voltage by a piezoelectric effect of a piezoelectric element such as a piezoelectric ceramic.

Piezoelectric transformers developed at the end of the 19th century have been developed as a boost transformer for high voltage sources. However, due to material limitations such as the breakdown strength of the piezoelectric ceramic material, development of the piezoelectric transformer was stopped without advancement of the commercialization of the piezoelectric transformer. 2. Description of the Related Art In recent years, there has been a growing demand for miniaturization and thinning of portable information devices such as bar-type personal computers, electronic notebooks, and game machines, which are under development of high-strength piezoelectric ceramics. As a step-up transformer of an inverter power source for a liquid crystal backlight mounted on the device, the piezoelectric transformer has received a great deal of attention as a result of such developments and demands.

The backlight inverter is used as a power source for a cold cathode fluorescent lamp used as a backlight source. The inverter requires a low DC voltage, such as 5V, 9V, or 12V, supplied from the battery, to be converted to a high frequency high voltage of about 1000 Vrms at lighting and about 500 Vrms at steady state. The electronic winding transformer, which is currently used as a backlight inverter, uses a horizontal structure with a special core to cope with recent thinning trends. However, there are limitations in realizing miniaturization and thinning for securing the withstand voltage. In addition, there is a disadvantage in that efficiency is lowered due to an increase in winding loss due to use of a copper wire having a large core loss.

On the other hand, the piezoelectric transformer has the following configuration. Primary (input side) and secondary (output side) electrodes are disposed on a piezoelectric ceramic material such as lead zirconate titanate or a piezoelectric crystal material such as lithium niobate. An AC voltage having a frequency near the resonance frequency of the piezoelectric transformer is applied to the primary side, and the piezoelectric transformer is mechanically vibrated. This mechanical vibration is converted by the piezoelectric effect and is taken out from the electrode on the secondary side in the form of high-pressure generated power. Such a piezoelectric transformer can realize thinning, and can be thinner than an electromagnetic transformer. In addition, a piezoelectric transformer can achieve high conversion efficiency.

Hereinafter, a conventional cold cathode fluorescent lamp driving apparatus using a piezoelectric transformer will be described with reference to the related drawings.

20 is a schematic view of a Rosen-type piezoelectric transformer. The piezoelectric element is a piezoelectric ceramic material in which the electrodes on the primary side (input side) and the secondary side (output side) are made of piezoelectric ceramics such as lead zirconate titanate (PZT) On the spherical plate. The primary side is polarized in the thickness direction of the spherical plate and the secondary side is polarized in the longitudinal direction as indicated by P in the drawing. When an AC voltage having a frequency near the resonance frequency of the piezoelectric transformer is applied to the primary electrode, the piezoelectric transformer vibrates mechanically in the longitudinal direction. This mechanical vibration is converted into a voltage by the piezoelectric effect, and the high-voltage generated power is taken out from the secondary side.

21 is a block diagram of a conventional driving circuit for a piezoelectric transformer shown in FIG. 20, that is, a conventional cold-cathode fluorescent lamp driving circuit using a piezoelectric transformer. A conventional system for driving a piezoelectric transformer includes a self-excited oscillating circuit system and a take-off oscillating circuit system. The self-excited oscillation circuit system has a problem in conversion efficiency and can not follow the large fluctuation of the load. For this reason, in the conventional example of the present invention, a take-in oscillation circuit system is usually used. The drive circuit shown in Fig. 21 is also a drive circuit of the take-off system.

21, the variable oscillation circuit 101 generates an AC drive signal having a frequency near the resonance frequency of the piezoelectric transformer 104. [ The output signal of the variable oscillation circuit 101 is waveform-shaped in the form of a substantially sinusoidal wave by the waveform shaping circuit 102 in order to reduce the loss of the piezoelectric transformer 104. [ As the waveform shaping circuit 102, a band pass filter is used in a simple case and a band pass filter is used when efficiency is important. The output of the waveform shaping circuit 102 is subjected to current amplification or voltage amplification so that the drive circuit 103 has a level enough to drive the piezoelectric transformer. The drive circuit 103 is constituted by only a normal amplification circuit made of a transistor A combination of an amplifying circuit and a step-up transformer. The output of the drive circuit 103 is boosted by the piezoelectric transformer 104 and then applied to the cold-cathode fluorescent lamp 105 so that the cold-cathode fluorescent lamp 105 is turned on.

The resonant frequency of the piezoelectric transformer 104 changes due to environmental changes such as temperature and load. Therefore, when the piezoelectric transformer is driven by a certain frequency like the circuit shown in Fig. 21, the relationship between the piezoelectric transformer and the drive frequency is changed. When the driving frequency exhibits a large deviation from the resonance frequency of the piezoelectric transformer, the step-up ratio of the piezoelectric transformer is significantly reduced, and sufficient current can not flow through the cold-cathode fluorescent lamp 105. Therefore, the cold-cathode fluorescent lamp 105 can not maintain sufficient brightness.

The circuit shown in FIG. 22 can correspond to the change in the resonant frequency of the piezoelectric transformer 104. FIG. 22 is a block diagram of another conventional driving circuit of the piezoelectric transformer 104 shown in FIG. 20, that is, a cold cathode fluorescent lamp driving apparatus using a piezoelectric transformer. Here, the functions of the variable oscillation circuit 101, the waveform shaping circuit 102, the drive circuit 103, and the piezoelectric transformer 104 are the same as those of the circuit shown in FIG. A feedback resistor 106 having a small resistance in series is connected to the cold-cathode fluorescent lamp 105 in the circuit shown in FIG. 22, so that the current flowing through the cold- do. The voltage across the feedback resistor 106 is input to the oscillation control circuit 107. The oscillation control circuit 107 controls the output frequency of the variable oscillation circuit 101 so that the feedback resistance 106 becomes constant, that is, the cold-cathode fluorescent lamp 105 becomes constant. As a result of the control, the cold-cathode fluorescent lamp 105 is lit at a substantially constant brightness. At this time, the driving frequency is maintained to have a substantially constant relationship with the resonant frequency of the piezoelectric transformer.

In the above, the drive circuit of the ride-on oscillation circuit system has been described as a conventional piezoelectric transformer drive device.

However, when the cold-cathode fluorescent lamp is driven by the AC voltage, the characteristics, that is, the absolute value and the phase of the impedance are remarkably changed. When the cold-cathode fluorescent lamp is driven by the high-frequency AC voltage, the change is considerably large and complicated. Also, as the diameter of the tube decreases, such tendency becomes larger. In the above-described conventional piezoelectric transformer, the above-described change of the cold-cathode fluorescent lamp is not considered. Therefore, the conventional driving apparatus can not cope with such a change and the current flowing through the cold-cathode fluorescent lamp pulsates, so that the brightness can not be kept constant. As a result, the reliability of the cold-cathode fluorescent lamp is lowered and the lifetime of the fluorescent lamp is shortened.

When the current flowing through the cold-cathode fluorescent lamp is pulsated, it is impossible to control the current flowing through the cold-cathode fluorescent lamp to be constant in the driving apparatus shown in FIG. Therefore, the driving frequency can not maintain a substantially constant relationship with the resonant frequency of the piezoelectric transformer, so that the driving efficiency of the piezoelectric transformer is lowered and the efficiency of the cold cathode fluorescent lamp driving apparatus using the piezoelectric transformer is lowered. In addition, the piezoelectric transformer is greatly disturbed by pulsation, and the heat generation is increased. As a result, there is a problem that the reliability significantly deteriorates.

Accordingly, an object of the present invention is to provide a cold-cathode fluorescent lamp that uses a piezoelectric transformer to suppress pulsation of a current flowing through a cold-cathode fluorescent lamp so as to improve the controllability of the current flowing through the cold-cathode fluorescent lamp, And to provide a driving apparatus.

Another object of the present invention is to provide a cold cathode fluorescent lamp driving apparatus using a piezoelectric element which improves driving efficiency and reliability of a cold-cathode fluorescent lamp and a piezoelectric transformer, thereby extending their service life and satisfying all conditions of high driving efficiency, high reliability and long life .

According to a first aspect of the present invention, there is provided an oscillation circuit comprising: an oscillation circuit for generating an AC drive signal; A drive circuit for amplifying the AC drive signal; A piezoelectric transformer in which an input electrode and an output electrode are disposed on a piezoelectric element; A cold cathode fluorescent lamp driving device using a piezoelectric transformer having a cold cathode fluorescent lamp and in which a current limiting resistor is connected in series between the output of the amplifying circuit and the input electrode of the piezoelectric transformer.

A second embodiment of the present invention includes an oscillation circuit for generating an AC drive signal; A drive circuit for amplifying the AC drive signal; A piezoelectric transformer in which an input electrode and an output electrode are disposed on a piezoelectric element; A cold cathode fluorescent lamp driving apparatus using a piezoelectric transformer having a cold cathode fluorescent lamp and in which a current limiting resistor is connected in series between the output electrode of the piezoelectric transformer and the cold cathode fluorescent lamp.

According to a third aspect of the present invention, there is provided an oscillation circuit comprising: an oscillation circuit for generating an AC drive signal; A drive circuit for amplifying the AC drive signal; A piezoelectric transformer in which an input electrode and an output electrode are disposed on a piezoelectric element; A cold cathode fluorescent lamp, and the driving circuit includes a current amplifying circuit and a step-up transformer, and the output impedance of the step-up transformer is about 5% to 20% of the input impedance of the piezoelectric transformer. do.

A fourth embodiment of the present invention is an oscillation circuit comprising: an oscillation circuit for generating an AC drive signal; A drive circuit for amplifying the AC drive signal; A piezoelectric transformer in which an input electrode and an output electrode are disposed on a piezoelectric element; Cathode fluorescent lamp, and a capacitor for load balancing is connected in series to the base potential side of the cold-cathode fluorescent lamp, thereby realizing a cold-cathode fluorescent lamp driving apparatus using a piezoelectric transformer.

A fifth embodiment of the present invention is an oscillation circuit comprising: an oscillation circuit for generating an AC drive signal; A drive circuit for amplifying the AC drive signal; A piezoelectric transformer in which an input electrode and an output electrode are disposed on a piezoelectric element; A cold cathode fluorescent lamp driving apparatus using a piezoelectric transformer having a cold cathode fluorescent lamp, a piezoelectric transformer having a balanced output, and a cold cathode fluorescent lamp connected to a balanced output.

According to the first invention of the present invention, in order to suppress the fluctuation of the characteristic of the cold-cathode fluorescent lamp, for example, a resistor having a value in the range of several to several tens of percent of the piezoelectric transformer is connected between the drive circuit and the input terminal of the piezoelectric transformer. Even when the impedance of the cold-cathode fluorescent lamp is decreased due to the connection of the resistor, the piezoelectric transformer can not supply a large current. Therefore, the value of the current flowing through the cold-cathode fluorescent lamp can be kept substantially constant, so that the pulsation can be suppressed.

According to the second invention of the present invention, in order to suppress the fluctuation of the characteristics of the cold-cathode fluorescent lamp, for example, a resistor having a value in the range of several to several tens percent of the input impedance of the cold-cathode fluorescent lamp is connected to the input terminal of the piezoelectric transformer, Respectively. Even when the impedance of the cold-cathode fluorescent lamp is decreased due to the connection of the resistor, the piezoelectric transformer can not supply a large current. Therefore, the value of the current flowing through the cold-cathode fluorescent lamp can be kept substantially constant, so that the pulsation can be suppressed.

According to the third invention of the present invention, the electromagnetic step-up transformer is connected between the drive circuit and the input terminal of the piezoelectric transformer, the output impedance of the step-up transformer is set high, or is set in the range of several to several tens of percent of the input impedance of the piezoelectric transformer. As a result, even when the impedance of the cold-cathode fluorescent lamp is reduced, the piezoelectric transformer can not supply a large current. As a result, the value of the current flowing through the cold-cathode fluorescent lamp can be kept substantially constant, so that the lamp can be suppressed.

According to the fourth invention of the present invention, the capacitor is connected in series between the cold-cathode fluorescent lamp and the common level. Thus, the cold-cathode fluorescent lamps have their respective terminals connected to the output capacitance of the piezoelectric transformer and the capacitance of the capacitor, respectively. Thus, the pulsation of the current of the cold-cathode fluorescent lamp can be suppressed and the value of the current flowing through the cold-cathode fluorescent lamp can be kept substantially constant.

According to the fifth invention of the present invention, a piezoelectric transformer having a balanced output is used, and variation in characteristics of the cold-cathode fluorescent lamp can be suppressed. Therefore, the value of the current flowing through the cold-cathode fluorescent lamp can be kept substantially constant and the pulsation can be suppressed, so that the cold-cathode fluorescent lamp driving apparatus using the piezoelectric transformer can be stably operated.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]

1 is a block diagram showing a cold-cathode fluorescent lamp driving apparatus using a piezoelectric transformer, that is, an inverter circuit. In the figure, the piezoelectric transformer 5 is a piezo-electric transformer of a predetermined type, that is, a rosen type or another type. The variable oscillation circuit 1 generates an AC drive signal having a frequency close to the resonance frequency of the piezoelectric transformer 5. When the piezoelectric transformer 5 is driven by a drive signal of a square wave, components other than frequencies near the resonant frequency are converted into heat in the piezoelectric transformer 5. In view of the reliability and conversion efficiency of the piezoelectric transformer 5, The waveform of the output signal of the waveform shaping circuit 1 becomes a substantially sinusoidal waveform by the waveform shaping circuit 2. [ In a simple case, the waveform shaping circuit 2 is a low-power filter. When the efficiency is particularly important, a band-pass filter is used for the waveform shaping circuit 2. The output of the waveform shaping circuit 2 is subjected to current amplification or voltage amplification by a drive circuit so as to be amplified to a level sufficient to drive the piezoelectric transformer 5. [ The driving circuit 3 is constituted only by a normal amplifying circuit made of a transistor or by a combination of an amplifying circuit and a step-up transformer. The output of the drive circuit 3 is input to the piezoelectric transformer 5 through the resistor 4. [ The piezoelectric transformer 5 boosts the input voltage by the piezoelectric effect. An output signal which is a high voltage of the piezoelectric transformer 5 is applied to the cold-cathode fluorescent lamp 6 so as to light the cold-cathode fluorescent lamp 6.

In the cold-cathode fluorescent lamp driving circuit using the piezoelectric transformer 5 as shown in Fig. 1, the driving frequency is usually set to about 50 to 200 kHz. When such a high frequency is used to drive the cold-cathode fluorescent lamp 6, the cold-cathode fluorescent lamp 6 exhibits a complicated phenomenon. That is, the absolute value of the impedance and the phase change unstably. Even when an alternating voltage having a constant amplitude is used during driving, the current flowing through the cold-cathode fluorescent lamp 6 changes unstably as shown in FIG. That is, it causes pulsation. In FIG. 2, the abscissa represents the time and the vertical side represents the value of the current flowing through the cold-cathode fluorescent lamp 6. In order to clearly show the pulsation, the envelope of the current waveform is shown. The period of the current change is approximately several hundred to several thousand Hz. And the magnitude of the change ranges from a few percent to a few dozen percent. As the driving frequency increases or as the diameter of the fluorescent lamp decreases, the tendency of instability increases. When the instability of the cold-cathode fluorescent lamp 5 is increased, the piezoelectric transformer 6 can withstand load fluctuations. Therefore, a larger operation instability is generated in the circuit, and the heat generation of the piezoelectric transformer 5 is increased, so that the characteristics are lowered and the service life is shortened. In addition, the brightness of the cold-cathode fluorescent lamp 6 becomes unstable and the life span is likewise shortened.

In the cold cathode fluorescent lamp driving apparatus using the piezoelectric transformer shown in Fig. 1, the resistor 4 is connected between the drive circuit 3 and the input terminal of the piezoelectric transformer 5. [ When the impedance of the cold-cathode fluorescent lamp 6 is reduced, the piezoelectric transformer 5 can not supply a large current due to the connection of the current limiting resistor 4. As a result, the value of the current flowing through the cold-cathode fluorescent lamp 6 can be kept substantially constant as shown in Fig. In FIG. 3, the abscissa represents the time and the ordinate represents the value of the current flowing through the cold-cathode fluorescent lamp 6. The input current of the piezoelectric transformer is limited, so that the output current of the piezoelectric transformer is also limited, so that the pulsation of the current flowing through the cold-cathode fluorescent lamp 6 can be suppressed as shown in Fig. As the resistance of the resistor 4 increases, the effect of suppressing the pulsation of the current is increased, but the loss due to the resistor 4 is increased and the efficiency of the driving circuit is lowered. Therefore, the resistance value can be appropriately determined in consideration of the magnitude of the ripple and the driving efficiency. For example, a range of several to several tens of percent of the input impedance of the piezoelectric transformer 5 can be used as a guide. When the resistance value is about 5% to 20%, the efficiency and stability requirements can be satisfied.

4 is a block diagram of another example of a cold cathode fluorescent lamp driving apparatus using a piezoelectric transformer, that is, an inverter circuit. In the figure, the variable oscillation circuit 1, the waveform shaping circuit 2, the drive circuit 3, the resistor 4, the piezoelectric transformer 5 and the cold-cathode fluorescent lamp 6 are the same as the example shown in Fig. Function. The resonant frequency of the piezoelectric transformer varies depending on environmental changes such as temperature and load. When the piezoelectric transformer 5 is driven at a constant frequency as in the circuit shown in Fig. 1, the relationship between the resonant frequency of the piezoelectric transformer 5 and the drive frequency is changed. If the driving frequency exhibits a large deviation from the resonant frequency of the piezoelectric transformer, the step-up ratio of the piezoelectric transformer is significantly reduced. As a result, a sufficient current can not flow through the cold-cathode fluorescent lamp 6, and the cold-cathode fluorescent lamp 6 can not maintain sufficient brightness.

The circuit shown in Fig. 4 can cope with the fluctuation of the resonance frequency of the piezoelectric transformer 5 according to the environment. The cold cathode fluorescent lamps 6 are connected in series with a feedback resistor 7 having a small resistance. The feedback resistance 7 is used to detect the current flowing through the cold-cathode fluorescent lamp 6. The voltage across the feedback resistor is input to the oscillation control circuit 8. The oscillation control circuit 8 controls the frequency of the output signal of the variable oscillation circuit 1 so that the voltage across the feedback resistor 7 becomes constant, that is, the current flowing through the cold-cathode fluorescent lamp becomes constant. As a result of this control, the cold-cathode fluorescent lamp 6 is lit at a substantially constant brightness. At this time, if the resistor is not connected, the impedance of the cold-cathode fluorescent lamp 6 changes and the current flowing through the cold-cathode fluorescent lamp 6 changes unstably as shown in FIG. 2, The frequency of the output signal of the variable oscillation circuit 1 can not be controlled so that the flowing current becomes constant. In other words, the pulsation of the current flowing through the cold-cathode fluorescent lamp 60 can be suppressed by connecting a resistor between the drive circuit 3 and the input terminal of the piezoelectric transformer 5. Therefore, the cold- The frequency of the output signal of the variable oscillation circuit 1 can be controlled so that the current flowing through the variable oscillation circuit 1 becomes constant.

[Second Embodiment]

5 is a block diagram showing a cold cathode fluorescent lamp driving apparatus using a piezoelectric transformer, that is, an inverter circuit according to the second embodiment of the present invention. In the figure, the piezoelectric transformer 5 is a piezo-electric transformer of a predetermined type, that is, a rosen type or another type. The variable oscillation circuit 1 generates an AC drive signal having a frequency close to the resonance frequency of the piezoelectric transformer 5. When the piezoelectric transformer 5 is driven by a drive signal of a square wave, components other than frequencies near the resonance frequency are converted into heat in the piezoelectric transformer 5 without contributing to voltage conversion. In view of the reliability and conversion efficiency of the piezoelectric transformer 5, the waveform of the output signal of the variable oscillation circuit 1 becomes substantially sinusoidal by the waveform shaping circuit 2. [ In a simple case, the waveform shaping circuit 2 is a low-pass filter. When the efficiency is particularly important, a band-pass filter is used for the waveform shaping circuit 2. The output of the waveform shaping circuit 2 is subjected to current amplification or voltage amplification by a drive circuit so as to be amplified to a level sufficient to drive the piezoelectric transformer 5. [ The driving circuit 3 is constituted only by a normal amplifying circuit made of a transistor or by a combination of an amplifying circuit and a step-up transformer. The output of the drive circuit 3 is input to the drive electrode (input electrode) of the piezoelectric transformer 5. The piezoelectric transformer 5 boosts the input voltage by the piezoelectric effect. The output signal of the piezoelectric transformer is applied to the cold-cathode fluorescent lamp 6 through the resistor 9). The negative fluorescent lamp (6) stably lights up by the function of the resistor (9).

In the inverter circuit using the piezoelectric transformer 5 as shown in FIG. 5, the driving frequency is usually set to about 50 to 200 kHz in accordance with the easy production of the piezoelectric transformer 5. When such a high frequency is used to drive the cold-cathode fluorescent lamp 6, the cold-cathode fluorescent lamp 6 exhibits a complicated phenomenon. For example, the absolute value and phase of the impedance change unstably. Even when an alternating voltage having a constant amplitude is used during driving, the current flowing through the cold-cathode fluorescent lamp 6 changes unstably as shown in FIG. That is, it causes pulsation. In FIG. 2, the abscissa represents time and the ordinate represents the envelope of the current waveform flowing through the cold-cathode fluorescent lamp 6. The period of the current change is approximately several hundred to several thousand Hz. And the magnitude of the change ranges from a few percent to a few dozen percent. As the driving frequency increases, or as the tube diameter of the fluorescent lamp decreases, the tendency of instability increases. When the instability of the cold-cathode fluorescent lamp 5 is increased, the piezoelectric transformer 6 can withstand load fluctuations. Therefore, a larger operation instability is generated and the heat generation of the piezoelectric transformer 5 is increased, so that the characteristics are lowered and the service life is shortened. In addition, the brightness of the cold-cathode fluorescent lamp 6 becomes unstable and the life span is likewise shortened.

5, the resistor 4 is connected between the output terminal of the piezoelectric transformer 5 and the cold-cathode fluorescent lamp 6. In the driving circuit shown in Fig. When the impedance of the cold-cathode fluorescent lamp 6 is reduced, the piezoelectric transformer 5 can not supply a large current due to the connection of the resistor 9. As a result, the value of the current flowing through the cold-cathode fluorescent lamp 6 can be kept substantially constant as shown in Fig. In FIG. 3, the abscissa represents time and the ordinate represents the envelope of the current waveform flowing through the cold-cathode fluorescent lamp 6. The output current of the piezoelectric transformer is limited, so that the pulsation of the current flowing through the cold-cathode fluorescent lamp 6 can be suppressed as shown in Fig. As the resistance value of the resistor 9 increases, the effect of suppressing the pulsation of the current is increased, but the loss due to the resistor 4 is increased and the efficiency of the driving circuit is lowered. Therefore, the resistance value can be appropriately determined in consideration of the magnitude of the ripple and the driving efficiency. For example, a range of several to several tens of percent of the input impedance of the piezoelectric transformer 5 can be used as a guide. When the resistance value is about 5% to 20%, the efficiency and stability requirements can be satisfied.

6 is a block diagram of another example of a cold cathode fluorescent lamp driving apparatus using a piezoelectric transformer, that is, an inverter circuit. In the figure, the variable oscillation circuit 1, the waveform shaping circuit 2, the drive circuit 3, the resistor 4, the piezoelectric transformer 5 and the cold-cathode fluorescent lamp 6 are the same as the example shown in Fig. Function. The resonant frequency of the piezoelectric transformer varies depending on environmental changes such as temperature and load. When the piezoelectric transformer 5 is driven at a constant frequency as in the circuit shown in Fig. 1, the relationship between the resonant frequency of the piezoelectric transformer 5 and the drive frequency is changed. If the driving frequency exhibits a large deviation from the resonant frequency of the piezoelectric transformer, the step-up ratio of the piezoelectric transformer is significantly reduced. As a result, a sufficient current can not flow through the cold-cathode fluorescent lamp 6, and the cold-cathode fluorescent lamp 6 can not maintain sufficient brightness.

The circuit shown in Fig. 6 can cope with a change in the resonant frequency of the piezoelectric transformer 5 depending on the environment. A cold cathode fluorescent lamp (6) is connected in series with a feedback resistor (7) having a small resistance. The feedback resistance 7 is used to detect the current flowing through the cold-cathode fluorescent lamp 6. The voltage across the feedback resistor is input to the oscillation control circuit 8. The oscillation control circuit 8 controls the frequency of the output signal of the variable oscillation circuit 1 so that the voltage across the feedback resistor 7 becomes constant, that is, the current flowing through the cold-cathode fluorescent lamp becomes constant. As a result of this control, the cold-cathode fluorescent lamp 6 is lit at a substantially constant brightness. At this time, if the resistor is not connected, the impedance of the cold-cathode fluorescent lamp 6 changes and the current flowing through the cold-cathode fluorescent lamp 6 changes unstably as shown in FIG. 2, The frequency of the output signal of the variable oscillation circuit 1 can not be controlled so that the flowing current becomes constant. In other words, the pulsation of the current flowing through the cold-cathode fluorescent lamp 6 can be suppressed by connecting a resistor between the drive circuit 3 and the input terminal of the piezoelectric transformer 5. Therefore, the frequency of the output signal of the variable oscillation circuit 1 can be stably controlled so that the current flowing through the cold-cathode fluorescent lamp 6 becomes constant.

7 is a block diagram of another example of a cold cathode fluorescent lamp driving apparatus using a piezoelectric transformer, that is, an inverter circuit. In the figure, the variable oscillation circuit 1, the waveform shaping circuit 2, the drive circuit 3, the resistor 4, the piezoelectric transformer 5 and the cold-cathode fluorescent lamp 6 are the same as the example shown in Fig. Function. The circuit shown in the figure may correspond to a change in the resonant frequency of the piezoelectric transformer 5 depending on the environment. A feedback resistor (10) is connected in series to the cold-cathode fluorescent lamp (6). The feedback resistance 10 is used to detect the current flowing through the cold-cathode fluorescent lamp 6 and suppresses the pulsation of the current flowing through the cold-cathode fluorescent lamp 6. As the resistance value of the feedback resistor 10 increases, the effect of suppressing the pulsation of the current increases, but the loss due to the resistor 10 increases, so that the efficiency of the driving circuit decreases. Therefore, the resistance value should be appropriately selected in consideration of the magnitude of the pulsation and the driving efficiency. For example, a range of several to several tens of percent of the input impedance of the cold-cathode fluorescent lamp 6 in the driving state is used as a guide.

The voltage across the feedback resistor 10 is divided by the dividing resistors 11 and 12 and input to the oscillation control circuit 8. [ The oscillation control circuit 8 controls the frequency of the output signal of the variable oscillation circuit 1 so that the voltage across the feedback resistor 10 is constant, that is, the current flowing through the cold-cathode fluorescent lamp 6 is kept constant. As a result of this control, the cold-cathode fluorescent lamp 6 is lit at a substantially constant brightness. In other words, even when the impedance of the cold-cathode fluorescent lamp 6 is complicatedly changed, the feedback resistor 10 suppresses the pulsation of the current flowing through the cold-cathode fluorescent lamp 6. Therefore, the frequency of the output signal of the variable oscillation circuit 1 can be controlled so that the current flowing through the cold-cathode fluorescent lamp 6 becomes constant.

[Third Embodiment]

FIG. 8 is a block diagram showing a cold cathode fluorescent lamp driving apparatus using a piezoelectric transformer, that is, an inverter circuit according to an example of the third embodiment of the present invention. In the figure, the piezoelectric transformer 5 is a piezo-electric transformer of a predetermined type, that is, a rosen type or another type. The variable oscillation circuit 1 generates an AC drive signal having a frequency close to the resonance frequency of the piezoelectric transformer 5. When the piezoelectric transformer 5 is driven by a drive signal of a square wave, components other than the frequency near the resonance frequency are converted into heat in the piezoelectric transformer 5. In view of the reliability and conversion efficiency of the piezoelectric transformer 5, the waveform of the output signal of the variable oscillation circuit 1 becomes substantially sinusoidal by the waveform shaping circuit 2. [ In a simple case, the waveform shaping circuit 2 is a low-pass filter. When the efficiency is particularly important, a band-pass filter is used for the waveform shaping circuit 2. The output of the waveform shaping circuit 2 is subjected to current amplification or voltage amplification by the drive circuit 3 so as to be amplified to a level sufficient to drive the piezoelectric transformer 5. The output of the drive circuit 3 is input to the piezoelectric transformer 5. The piezoelectric transformer 5 boosts the input voltage by the piezoelectric effect. The output signal of the piezoelectric transformer 5 is applied to the cold-cathode fluorescent lamp 6 so that the cold-cathode fluorescent lamp 6 is turned on.

In the inverter circuit using the piezoelectric transformer 5 as shown in Fig. 8, the driving frequency is usually set to about 50 to 200 kHz. When such a high frequency is used to drive the cold-cathode fluorescent lamp 6, The negative fluorescent lamp 6 exhibits a complicated phenomenon. For example, the absolute value and phase of the impedance change unstably. Even when an AC voltage having a constant amplitude is used during driving, the current flowing through the cold-cathode fluorescent lamp 6 causes unstable pulsation as shown in Fig. In FIG. 2, the horizontal side represents time and the vertical axis represents the envelope of the current waveform flowing through the cold-cathode fluorescent lamp 6. The period of the current change is approximately several hundred to several thousand Hz. And the magnitude of the change ranges from a few percent to a few tens of percent of the maximum current. As the driving frequency increases, or as the tube diameter of the fluorescent lamp decreases, the tendency of instability increases. When the instability of the cold-cathode fluorescent lamp 5 is increased, the piezoelectric transformer 6 can withstand load fluctuations. Therefore, a larger operation instability is generated and the heat generation of the piezoelectric transformer 5 is increased, so that the characteristics are lowered and the service life is shortened. In addition, the brightness of the cold-cathode fluorescent lamp 6 becomes unstable and the life span is likewise shortened.

8, an electromagnetic step-up transformer 14 is connected between the drive circuit 3 and the input terminal of the piezoelectric transformer 5. In the drive circuit shown in Fig. The output impedance of the step-up transformer 14 is set high. Even when the impedance of the cold-cathode fluorescent lamp 6 is reduced, the piezoelectric transformer 5 can not supply a large current. As a result, the value of the current flowing through the cold-cathode fluorescent lamp 6 can be kept substantially constant as shown in Fig. In the graph of FIG. 3, the abscissa represents the time and the ordinate represents the envelope of the current waveform flowing through the cold-cathode fluorescent lamp 6. The input current of the piezoelectric transformer is limited, so that the pulsation of the current flowing through the cold-cathode fluorescent lamp 6 can be suppressed as shown in FIG. 2. As the output impedance of the step-up transformer 14 increases, But the loss due to the step-up transformer 14 is increased, and the efficiency with the driving circuit is lowered. Therefore, the impedance value of the step-up transformer can be appropriately determined in consideration of the magnitude of the ripple and the drive efficiency. For example, the impedance of the step-up transformer 14 may be adjusted by a winding or a core so as to be in a range of several tens to several ten percent of the input impedance of the piezoelectric transformer 5. [

Fig. 9 is a block diagram of another example of a cold cathode fluorescent lamp driving apparatus using a piezoelectric transformer, that is, an inverter circuit. In the figure, the variable oscillation circuit 1, the waveform shaping circuit 2, the drive circuit 3, the resistor 4, the piezoelectric transformer 5 and the cold-cathode fluorescent lamp 6 are the same as the example shown in Fig. 8 Function. The resonant frequency of the piezoelectric transformer varies depending on environmental changes such as temperature and load. When the piezoelectric transformer 5 is driven at a constant frequency as in the circuit shown in Fig. 8, the relationship between the resonant frequency of the piezoelectric transformer 5 and the drive frequency is changed. If the driving frequency exhibits a large deviation from the resonant frequency of the piezoelectric transformer, the step-up ratio of the piezoelectric transformer is significantly reduced. As a result, a sufficient current can not flow through the cold-cathode fluorescent lamp 6, and the cold-cathode fluorescent lamp 6 can not maintain sufficient brightness.

The circuit shown in Fig. 9 can cope with a change in the resonant frequency of the piezoelectric transformer 5 depending on the environment. The cold cathode fluorescent lamp (6) is connected in series with a feedback resistor (7) having a small resistance. The feedback resistance 7 is used to detect the current flowing through the cold-cathode fluorescent lamp 6. The voltage across the feedback resistor 7 is input to the oscillation control circuit 8. [ The oscillation control circuit 8 controls the frequency of the output signal of the variable oscillation circuit 1 so that the voltage across the feedback resistor 7 becomes constant, that is, the current flowing through the cold-cathode fluorescent lamp becomes constant. As a result of this control, the cold-cathode fluorescent lamp 6 is lit at a substantially constant brightness. At this time, if the resistor 4 is not connected, the impedance of the cold-cathode fluorescent lamp 6 changes and the current flowing through the cold-cathode fluorescent lamp 6 changes unstably as shown in FIG. 2, It is impossible to control the frequency of the output signal of the variable oscillation circuit 1 so that the current flowing through the variable oscillation circuit 1 becomes constant. In other words, the pulsation of the current flowing through the cold-cathode fluorescent lamp 6 can be suppressed by connecting the resistor 4 between the drive circuit 3 and the input terminal of the piezoelectric transformer 5. Therefore, the frequency of the output signal of the variable oscillation circuit 1 can be stably controlled so that the current flowing through the cold-cathode fluorescent lamp 6 becomes constant.

10 is a block diagram of another example of a cold cathode fluorescent lamp driving apparatus using a piezoelectric transformer, that is, an inverter circuit. In the figure, the variable oscillation circuit 1, the waveform shaping circuit 2, the drive circuit 3, the resistor 4, the piezoelectric transformer 5 and the cold-cathode fluorescent lamp 6 are the same as the example shown in Fig. 8 Function. In the drive circuit shown in Fig. 10, the electromagnetic step-up transformer 14 is connected between the drive circuit 3 and the input terminal of the piezoelectric transformer 5. A resistor 15 is connected to the output of the step-up transformer 14. Even when the impedance of the cold-cathode fluorescent lamp 6 is reduced, the piezoelectric transformer 5 can not supply a large current. As a result, the value of the current flowing through the cold-cathode fluorescent lamp 6 can be kept substantially constant as shown in Fig. The input current of the piezoelectric transformer is limited, so that the pulsation of the current flowing through the cold-cathode fluorescent lamp 6 can be suppressed as shown in Fig. As the resistance value of the resistor 15 connected to the output of the step-up transformer 14 is increased, the effect of suppressing the pulsation of the current is increased, but the loss is increased and the efficiency of the driving circuit is lowered. Therefore, the resistance value should be appropriately determined in consideration of the magnitude of the pulsation and the driving efficiency. For example, the resistor 15 is adjusted to be in the range of several tens to several ten percent of the input impedance of the piezoelectric transformer 5.

In the circuit shown in Fig. 10, the resistor 15 is connected to the output of the step-up transformer 14. Fig. Instead of the resistor 15, a coil may be connected. The same effect can be obtained in such a configuration. As the inductance of the coil connected to the output of the step-up transformer 14 increases, the effect of suppressing the pulsation of the current increases, but the loss increases and the efficiency of the drive circuit decreases. Therefore, an appropriate impedance should be determined in consideration of the magnitude of pulsation and the driving efficiency. For example, the impedance of the coil is adjusted to be in the range of several tens to several ten percent of the input impedance of the piezoelectric transformer 5. For example, when the impedance is about 5% to 20%, the efficiency and stability requirements can be satisfied.

The circuit shown in Fig. 10 can correspond to the change in the resonant frequency of the piezoelectric transformer 5 depending on the environment. The feedback resistance is connected in series to the cold-cathode fluorescent lamp (6). The feedback resistance is used to detect the current flowing through the cold-cathode fluorescent lamp 6. In this configuration, since it is easy to control the frequency of the output signal of the variable oscillation circuit 1, the voltage across the feedback resistance is constant, that is, the current flowing through the cold-cathode fluorescent lamp becomes constant.

[Fourth Embodiment]

FIG. 11 is a block diagram showing a cold cathode fluorescent lamp driving apparatus using a piezoelectric transformer, that is, an inverter circuit according to an example of the fourth embodiment of the present invention; In the figure, the piezoelectric transformer 5 is a piezo-electric transformer of a predetermined type, that is, a rosen type or another type. The variable oscillation circuit 1 generates an AC drive signal having a frequency close to the resonance frequency of the piezoelectric transformer 5. When the piezoelectric transformer 5 is driven by a drive signal of a square wave, components other than the frequency near the resonance frequency are converted into heat in the piezoelectric transformer 5. In view of the reliability and conversion efficiency of the piezoelectric transformer 5, the waveform of the output signal of the variable oscillation circuit 1 becomes substantially sinusoidal by the waveform shaping circuit 2. [ In a simple case, the waveform shaping circuit 2 is a low-pass filter. When the efficiency is particularly important, a band-pass filter is used for the waveform shaping circuit 2. The output of the waveform shaping circuit 2 is subjected to current amplification or voltage amplification by the drive circuit 3 so as to be amplified to a level sufficient to drive the piezoelectric transformer 5. The drive circuit 3 is composed of a current amplifier 12 and a step-up transformer 13. The output of the drive circuit 3 is input to the piezoelectric transformer 5. The piezoelectric transformer 5 boosts the input voltage by the piezoelectric effect. The output signal of the piezoelectric transformer 5 is applied to the cold-cathode fluorescent lamp 6 so that the cold-cathode fluorescent lamp 6 is turned on.

In an inverter circuit using a piezoelectric transformer 5, a driving frequency is usually set to about 50 to 200 kHz. When such a high frequency is used to drive the cold-cathode fluorescent lamp 6, the cold-cathode fluorescent lamp 6 exhibits a complicated phenomenon. For example, the absolute value and phase of the impedance change unstably. Even when an AC voltage having a constant amplitude is used during driving, the current flowing through the cold-cathode fluorescent lamp 6 causes unstable pulsation as shown in Fig. In the graph of FIG. 2, the abscissa represents the time and the ordinate represents the envelope of the current waveform flowing through the cold-cathode fluorescent lamp 6. The period of the current change is approximately several hundred to several thousand Hz. And the magnitude of the change ranges from a few percent to a few tens of percent of the maximum current. As the driving frequency increases or as the diameter of the fluorescent lamp decreases, the tendency of instability increases. When the instability of the cold-cathode fluorescent lamp 5 is increased, the piezoelectric transformer 6 can withstand load fluctuations. Therefore, a larger operation instability is generated and the heat generation of the piezoelectric transformer 5 is increased, so that the characteristics are lowered and the service life is shortened. In addition, the brightness of the cold-cathode fluorescent lamp 6 becomes unstable and the life span is likewise shortened.

In the driving circuit shown in Fig. 11, the capacitor 16 is connected in series between the cold-cathode fluorescent lamp 6 and the common level. Thus, both terminals of the cold-cathode fluorescent lamp 6 are connected to the output capacitance of the piezoelectric transformer 5 and the capacitance of the capacitor 16. The cold-cathode fluorescent lamp 6 is connected to both terminals (capacitive loads) of the cold-cathode fluorescent lamp 6 for the purpose of balance. According to the present invention, such unstable operation can be suppressed when the cold-cathode fluorescent lamp 6 is first driven by the unbalanced loads, while the cold-cathode fluorescent lamp 6 is driven by the balanced loads . Since the capacitor 16 is connected in series between the cold-cathode fluorescent lamp 6 and the common level and both terminals of the cold-cathode fluorescent lamp 6 are driven to be connected to the balanced loads (capacitive loads) The pulsation of the current flowing through the cold-cathode fluorescent lamp 6 is suppressed. As a result, the value of the current flowing through the cold-cathode fluorescent lamp 6 can be made substantially constant as shown in FIG. In the graph of FIG. 3, the abscissa represents the time and the ordinate represents the envelope of the current waveform flowing through the cold-cathode fluorescent lamp 6. The above effect can be confirmed when the capacitance of the capacitor 16 is about 0.2 to 2 times the output capacitance of the piezoelectric transformer 6.

12 is a block diagram of another example of a cold cathode fluorescent lamp driving apparatus using a piezoelectric transformer, that is, an inverter circuit. In the figure, the variable oscillation circuit 1, the waveform shaping circuit 2, the drive circuit 3, the resistor 4, the piezoelectric transformer 5 and the cold-cathode fluorescent lamp 6 are the same as the example shown in Fig. Function. The circuit shown in the figure can correspond to a change in the resonant frequency of the piezoelectric transformer 5 depending on the environment. A cold cathode fluorescent lamp (6) is connected in series with a capacitor (17). The capacitor 17 is used to detect the current flowing through the cold-cathode fluorescent lamp 6 and suppresses the pulsation of the current flowing through the cold-cathode fluorescent lamp 6.

The voltage across the capacitor 17 is input to the oscillation control circuit 8. The oscillation control circuit 8 controls the frequency of the output signal of the variable oscillation circuit 1 so that the voltage across the capacitor 17 is constant, that is, the current flowing through the cold-cathode fluorescent lamp becomes constant. As a result of this control, the cold-cathode fluorescent lamp 6 is lit at a substantially constant brightness.

[Fifth Embodiment]

FIG. 13 is a view showing a configuration of a piezoelectric transformer according to an example of the fifth embodiment of the present invention, and is a view from the side of a transformer. The piezoelectric transformer 18 is formed on a spherical plate made of a piezoelectric ceramic material such as lead zirconate titanate (PZT) and electrodes on the primary side (input side, electrodes 1 and 2) Respectively. In the drawing, arrows indicate polarization directions. The primary side is polarized in the thickness direction of the spherical plate and the secondary side is polarized in the longitudinal direction. An electrode 2 on the primary side is connected to a common level and an AC voltage having a frequency near the resonance frequency of the piezoelectric transformer 16 is applied to the electrode 2. [ The piezoelectric transformer 18 vibrates mechanically in the longitudinal direction (half-wave mode). The mechanical vibration has a distribution represented by a displacement distribution curve of FIG. The mechanical vibration is converted into a voltage by the piezoelectric effect so that a high voltage is taken out from the electrodes 3 and 4, that is, the secondary electrode. Unlike the unbalanced output of the conventional piezoelectric transformer, the output of the piezoelectric transformer 20 is taken out from the electrodes 3 and 4 to the output (balanced output) having the opposite sign.

FIG. 14 is a block diagram showing a cold-cathode fluorescent lamp driving apparatus using a piezoelectric transformer 14, that is, an inverter circuit. In the figure, the piezoelectric transformer 18 is the same as that shown in Fig. The variable oscillation circuit 1 generates an AC drive signal having a frequency near the resonance frequency of the 2/1 wavelength mode of the piezoelectric transformer 18. [ When the piezoelectric transformer 18 is driven by a drive signal of a square wave, components other than the frequency near the resonance frequency are converted into heat in the piezoelectric transformer 18. [ In view of the reliability and conversion efficiency of the piezoelectric transformer 18, the waveform of the output signal of the variable oscillation circuit 1 becomes substantially sinusoidal waveform by the waveform shaping circuit 2. [ In a simple case, the waveform shaping circuit 2 is a low-pass filter. Band filter is used as the waveform shaping circuit (2). The output of the waveform shaping circuit 2 is subjected to current amplification or voltage amplification by a drive circuit so as to be amplified to a level sufficient to drive the piezoelectric transformer 18. [ The output of the drive circuit 3 is input to the electrodes 1 and 2 of the piezoelectric transformer 18. The piezoelectric transformer 18 boosts the input voltage to a high voltage by the piezoelectric effect. The output signal of the piezoelectric transformer 18 is taken out as a balanced signal at the electrodes 3 and 4 so as to light the cold-cathode fluorescent lamp 6, and the balanced signal is applied to the cold-cathode fluorescent lamp 6.

In the cold-cathode fluorescent lamp driving circuit using the piezoelectric transformer as shown in FIG. 13, the driving frequency is usually set to about 50 to 200 KHz. When the cold-cathode fluorescent lamp 6 is driven by a conventional piezoelectric transformer having an unbalanced output and a high frequency, the cold-cathode fluorescent lamp 6 exhibits a complicated phenomenon. For example, the absolute value and phase of the impedance change unstably. Even when an alternating voltage having a constant amplitude is used during driving, the current flowing through the cold-cathode fluorescent lamp 6 causes pulsation unstably as shown in Fig. In the graph of FIG. 2, the abscissa represents the time and the ordinate represents the envelope of the current waveform flowing through the cold-cathode fluorescent lamp 6. The period of the current change is approximately several hundred to several thousand Hz. And the magnitude of the change ranges from a few percent to a few tens of percent of the maximum current. As the driving frequency increases or as the diameter of the fluorescent lamp decreases, the tendency of instability increases. When the instability of the cold-cathode fluorescent lamp 6 is raised, the piezoelectric transformer having an unbalanced output is less resistant to load fluctuations. Therefore, a larger operation unstable state is generated in the circuit, and the heat generation of the piezoelectric transformer 5 is increased, so that the characteristics are lowered and the service life is shortened. In addition, the brightness of the cold-cathode fluorescent lamp 6 becomes unstable and the life span is likewise shortened.

In the driving circuit of FIG. 14 using the piezoelectric transformer shown in FIG. 13, the cold-cathode fluorescent lamp 6 is driven by the balanced output of the piezoelectric transformer 16. According to the present invention, such a unstable operation can be suppressed when the cold-cathode fluorescent lamp 6 is first driven by unbalanced loads, while the cold-cathode fluorescent lamp 6 is driven by balanced loads. . By using a piezoelectric transformer having a balanced output, the ripple of the current flowing through the cold-cathode fluorescent lamp 6 can be suppressed as shown in Fig. As a result, if the balanced output is used during driving, the value of the current flowing through the cold-cathode fluorescent lamp 6 can be substantially constant as shown in FIG. In the graph of FIG. 3, the abscissa represents the time and the ordinate represents the envelope of the current waveform flowing through the cold-cathode fluorescent lamp 6.

FIG. 15 is a view showing a configuration of a piezoelectric transformer according to an example of the fourth embodiment of the present invention, and is a view from the side of a transformer. The piezoelectric transformer 19 is a piezoelectric transformer in which electrodes on the primary side (input side, electrodes 1, 2 and 3) and electrodes on the secondary side (output side, electrodes 4 and 5) are made of a piezoelectric ceramic material such as lead zirconate titanate (PZT) And is placed on a plate. In the drawing, arrows indicate polarization directions. The primary side is polarized in the thickness direction of the spherical plate and the secondary side is polarized in the longitudinal direction. The electrodes 3 on the primary side are connected to a common level, and an AC voltage having a frequency near the resonance frequency of the piezoelectric transformer 19 is applied to the electrodes 1 and 2. The piezoelectric transformer 19 vibrates mechanically in the longitudinal direction (one wavelength mode). The mechanical vibration has a distribution represented by a displacement distribution curve of FIG. The mechanical vibration is converted into a voltage by a piezoelectric effect so that a high voltage is taken out from the electrodes 4 and 5, that is, the secondary electrode. Unlike the unbalanced output of the conventional piezoelectric transformer, the output of the piezoelectric transformer 20 is taken out from the electrodes 4 and 5 to the output (balanced output) having the opposite sign.

FIG. 16 is a view showing a configuration of a piezoelectric transformer according to an example of the fourth embodiment of the present invention, and is a view from the side of a transformer. The piezoelectric transformer 20 is a piezoelectric transformer in which electrodes on the primary side (input side, electrodes 1, 2, 3, 4 and 5) and electrodes on the secondary side (output side, electrodes 6 and 7) are made of piezoelectric ceramics such as lead zirconate titanate (PZT) And is placed on a spherical plate made of a material. In the drawing, arrows indicate polarization directions. The primary side is polarized in the thickness direction of the spherical plate and the secondary side is polarized in the longitudinal direction. The electrodes 5 on the primary side are connected to a common level and an AC voltage having a frequency near the resonance frequency of the piezoelectric transformer 20 is applied to the electrodes 1, 2, 3 and 4. The piezoelectric transformer 20 vibrates mechanically in the longitudinal direction (3/2 wavelength mode). The mechanical vibration has a distribution represented by a displacement distribution curve of FIG. The mechanical vibration is converted into a voltage by the piezoelectric effect so that a high voltage is taken out from the electrodes 6 and 7, i.e., the secondary electrode. Unlike the unbalanced output of the conventional piezoelectric transformer, the output of the piezoelectric transformer 20 is taken out from the electrodes 6 and 7 to the output (balanced output) having the opposite sign.

FIG. 17 is a view showing a configuration of a piezoelectric transformer according to still another example of the fifth embodiment of the present invention, which is a side view of a transformer; FIG. The piezoelectric transformer 21 is formed on a spherical plate made of a piezoelectric ceramic material such as lead zirconate titanate (PZT), and electrodes on the primary side Respectively. In the drawing, arrows indicate polarization directions. The primary side is polarized in the thickness direction of the spherical plate and the secondary side is polarized in the longitudinal direction. An electrode 2 on the primary side is connected to a common level and an AC voltage having a frequency near the resonance frequency of the piezoelectric transformer 21 is applied to the electrode 1. [ The piezoelectric transformer 21 vibrates mechanically in the longitudinal direction (half-wave mode). The mechanical vibration has a distribution represented by a displacement distribution curve of FIG. The mechanical vibration is converted into a voltage by the piezoelectric effect so that a high voltage is taken out from the electrodes 3 and 4, that is, the secondary electrode. Unlike the unbalanced output of the conventional piezoelectric transformer, the output of the piezoelectric transformer 21 is taken out from the electrodes 3 and 4 to the output (balanced output) having the opposite sign.

The block diagram shows a cold-cathode fluorescent lamp driving apparatus using a piezoelectric transformer 21, that is, an inverter circuit. This is the same as that shown in Fig. 14, and a description thereof will be omitted. In the driving circuit using the piezoelectric transformer shown in FIG. 17, the cold-cathode fluorescent lamp 6 is driven by the balanced output of the piezoelectric transformer 21. According to the present invention, when cold cathode fluorescent lamps 6 are first driven by unbalanced loads, they operate unstably, whereas when cold cathode fluorescent lamps 6 are driven by balanced loads, such unstable operation can be suppressed . By using a piezoelectric transformer having a balanced output, the ripple of the current flowing through the cold-cathode fluorescent lamp 6 can be suppressed as shown in Fig. As a result, if the balanced output is used during driving, the value of the current flowing through the cold-cathode fluorescent lamp 6 can be substantially constant as shown in FIG. In the graph of FIG. 3, the abscissa represents the time and the ordinate represents the envelope of the current waveform flowing through the cold-cathode fluorescent lamp 6.

FIG. 18 is a view showing a configuration of a piezoelectric transformer according to another example of the fifth embodiment of the present invention, which is a side view of a transformer; FIG. The piezoelectric transformer 22 is formed on a spherical plate made of a piezoelectric ceramic material such as lead zirconate titanate (PZT), and electrodes on the primary side Respectively. In the drawing, arrows indicate polarization directions. The primary side is polarized in the thickness direction of the spherical plate and the secondary side is polarized in the longitudinal direction. An electrode 2 on the primary side is connected to a common level and an AC voltage having a frequency near the resonance frequency of the piezoelectric transformer 22 is applied to the electrode 1. [ The piezoelectric transformer 22 vibrates gas in the longitudinal direction (one-wave mode), and its mechanical vibration has a distribution represented by the displacement distribution curve of FIG. The mechanical vibration is converted into a voltage by the piezoelectric effect so that a high voltage is taken out from the electrodes 3 and 4, that is, the secondary electrode. Unlike the unbalanced output of the conventional piezoelectric transformer, the output of the piezoelectric transformer 22 is taken out from the electrodes 3 and 4 to the output (balanced output) having the opposite sign.

FIG. 19 is a view showing a configuration of a piezoelectric transformer according to still another example of the fifth embodiment of the present invention, which is a side view of a transformer. The piezoelectric transformer 23 is formed on a spherical plate made of a piezoelectric ceramic material such as lead zirconate titanate (PZT), and electrodes on the primary side Respectively. In the drawing, arrows indicate polarization directions. The primary side is polarized in the thickness direction of the spherical plate and the secondary side is polarized in the longitudinal direction. The electrode 2 on the primary side is connected to a common level and an AC voltage having a frequency near the resonant frequency of the piezoelectric transformer 23 is applied to the electrode 1. [ The piezoelectric transformer 23 vibrates mechanically in the longitudinal direction (3/2 wavelength mode). The mechanical vibration has a distribution represented by the displacement distribution curve of FIG. The mechanical vibration is converted into a voltage by the piezoelectric effect so that a high voltage is taken out from the electrodes 3 and 4, that is, the secondary electrode. Unlike the unbalanced output of the conventional piezoelectric transformer, the output of the piezoelectric transformer 22 is taken out from the electrodes 3 and 4 to the output (balanced output) having the opposite sign.

In the examples shown in FIGS. 17, 18 and 19, the output electrode is placed on the lower surface of the piezoelectric transformer. Alternatively, the output electrodes may be placed on the top surface of the piezoelectric transformer. In this case, the same effect can be obtained. On the other hand, the output electrode 3 may be arranged to be wound once around the piezoelectric transformer. In this case, the same effect can be obtained.

1 is a block diagram of an example of a cold cathode fluorescent lamp using a piezoelectric transformer according to a first embodiment of the present invention;

Fig. 2 is an envelope waveform diagram of a cold-cathode fluorescent lamp current in a cold-cathode fluorescent lamp driving apparatus using a piezoelectric transformer

3 is an envelope waveform diagram of the cold cathode fluorescent lamp current in the cold cathode fluorescent lamp driving apparatus using the piezoelectric transformer of the present invention

4 is a block diagram of another example of the first embodiment of the cold-cathode fluorescent lamp using the piezoelectric transformer according to the present invention

5 is a block diagram of an example of a cold cathode fluorescent lamp using a piezoelectric transformer according to a second embodiment of the present invention;

6 is a block diagram of another example of the second embodiment of the cold cathode fluorescent lamp using the piezoelectric transformer according to the present invention

7 is a block diagram of another example of the second embodiment of the cold cathode fluorescent lamp using the piezoelectric transformer according to the present invention

8 is a block diagram of an example of a third embodiment of a cold-cathode fluorescent lamp using a piezoelectric transformer according to the present invention

9 is a block diagram of another example of the third embodiment of the cold cathode fluorescent lamp using the piezoelectric transformer according to the present invention

10 is a block diagram of another example of the third embodiment of the cold-cathode fluorescent lamp using the piezoelectric transformer according to the present invention

11 is a block diagram of an example of the fourth embodiment of the cold cathode fluorescent lamp using the piezoelectric transformer according to the present invention

12 is a block diagram of another example of the fourth embodiment of the cold cathode fluorescent lamp using the piezoelectric transformer according to the present invention

FIG. 13 is a configuration diagram of a piezoelectric transformer used in an example of the fifth embodiment of the cold-cathode fluorescent lamp using the piezoelectric transformer according to the present invention

14 is a block diagram of an example of a fifth embodiment of a cold-cathode fluorescent lamp using the piezoelectric transformer according to the present invention

FIG. 15 is a block diagram of another piezoelectric transformer used in an example of the fifth embodiment of the cold-cathode fluorescent lamp using the piezoelectric transformer according to the present invention

FIG. 16 is a configuration diagram of another piezoelectric transformer used in the above example of the fifth embodiment of the cold-cathode fluorescent lamp using the piezoelectric transformer according to the present invention

17 is a view showing the configuration of the piezoelectric transformer used in the above example of the fifth embodiment of the cold-cathode fluorescent lamp using the piezoelectric transformer according to the present invention

FIG. 18 is a configuration diagram of the piezoelectric transformer used in the above example of the fifth embodiment of the cold-cathode fluorescent lamp using the piezoelectric transformer according to the present invention

FIG. 19 is a configuration diagram of the piezoelectric transformer used in the above example of the fifth embodiment of the cold-cathode fluorescent lamp using the piezoelectric transformer according to the present invention

20 shows the configuration of a conventional Rosen-type piezoelectric transformer

21 is a block diagram of a conventional cold cathode fluorescent lamp driving apparatus using a piezoelectric transformer;

22 is a block diagram of a conventional cold cathode fluorescent lamp driving apparatus using a piezoelectric transformer;

Description of the Related Art [0002]

1: variable oscillation circuit 2: waveform shaping circuit

3: Driver circuit 4: Resistance

5: Piezoelectric transformer 6: Cold-cathode fluorescent lamp

7: Feedback resistance 8: Oscillation control circuit

9: Resistance 10: Feedback resistance

11: partial pressure resistance 12: partial pressure resistance

13: current amplification circuit 14: electronic step-up circuit

15: Resistors 16 and 17: Capacitors

19, 20, 21, 22, 23: Piezoelectric transformers

Claims (12)

An oscillation circuit for generating an AC drive signal; A drive circuit for amplifying the AC drive signal; A piezoelectric transformer in which an input electrode and an output electrode are disposed on a piezoelectric element; A cold cathode fluorescent lamp drive device comprising a cold cathode fluorescent lamp, the cold cathode fluorescent lamp drive device comprising a resistor connected in series between an output of the amplifier drive circuit and an input electrode of the piezoelectric transformer, Fluorescent lamp drive. The method according to claim 1, An oscillation circuit for generating an AC drive signal; a drive circuit for amplifying the AC drive signal; A piezoelectric transformer in which an input electrode and an output electrode are disposed on a piezoelectric element; A cold cathode fluorescent lamp, Wherein a resistor having a value of about 5% to 20% of an input impedance of the piezoelectric transformer is connected in series between an output of the amplifier circuit and an input electrode of the piezoelectric transformer. drive. An oscillation circuit for generating an AC drive signal; A drive circuit for amplifying the AC drive signal; A piezoelectric transformer in which an input electrode and an output electrode are disposed on a piezoelectric element; A cold cathode fluorescent lamp, And a resistor is connected in series between the output electrode of the piezoelectric transformer and the cold-cathode fluorescent lamp. The method of claim 3, An oscillation circuit for generating an AC drive signal; A drive circuit for amplifying the AC drive signal; A piezoelectric transformer in which an input electrode and an output electrode are disposed on a piezoelectric element; A cold cathode fluorescent lamp, And a resistor having a value of about 5% to 20% of the impedance of the cold-cathode fluorescent lamp is connected in series between the output electrode of the piezoelectric transformer and the cold-cathode fluorescent lamp. . An oscillation circuit for generating an AC drive signal; A drive circuit for amplifying the AC drive signal; A piezoelectric transformer in which an input electrode and an output electrode are disposed on a piezoelectric element; A cold cathode fluorescent lamp, Wherein the drive circuit includes a current amplification circuit and a step-up transformer, and the output impedance of the step-up transformer is about 5% to 20% of the piezoelectric transformer. An oscillation circuit for generating an AC drive signal; A drive circuit for amplifying the AC drive signal; A piezoelectric transformer in which an input electrode and an output electrode are disposed on a piezoelectric element; A cold cathode fluorescent lamp, Wherein the driving circuit includes a current amplifying circuit and a step-up transformer, wherein a resistance or inductance is connected in series to an output terminal of the step-up transformer, and the resistance or inductance is about 5% to 20% of the input impedance of the piezoelectric transformer Wherein the cold cathode fluorescent lamp driving apparatus comprises a piezoelectric transformer. An oscillation circuit for generating an AC drive signal; A drive circuit for amplifying the AC drive signal; A piezoelectric transformer in which an input electrode and an output electrode are disposed on a piezoelectric element; A cold cathode fluorescent lamp, And a capacitor is connected in series to the base potential side of the cold-cathode fluorescent lamp. 8. The method of claim 7, An oscillation circuit for generating an AC drive signal; A drive circuit for amplifying the AC drive signal; A piezoelectric transformer in which an input electrode and an output electrode are disposed on a piezoelectric element; A cold cathode fluorescent lamp, Wherein a capacitor having a value about 0.2 to 2 times the output capacitance of the piezoelectric transformer is connected in series to the base potential side of the cold-cathode fluorescent lamp. An oscillation circuit for generating an AC drive signal; A drive circuit for amplifying the AC drive signal; A piezoelectric transformer in which an input electrode and an output electrode are disposed on a piezoelectric element; A cold cathode fluorescent lamp, Wherein the piezoelectric transformer has a balanced output and the cold-cathode fluorescent lamp is connected to the balanced output. 10. The method of claim 9, An oscillation circuit for generating an AC drive signal; A drive circuit for amplifying the AC drive signal; A piezoelectric transformer in which an input electrode and an output electrode are disposed on a piezoelectric element; A cold cathode fluorescent lamp, Wherein a balanced output is taken out at both ends by oscillating the piezoelectric transformer in the longitudinal direction, and the cold-cathode fluorescent lamp is connected to the balanced output. 10. The method of claim 9, An oscillation circuit for generating an AC drive signal; A drive circuit for amplifying the AC drive signal; A piezoelectric transformer in which an input electrode and an output electrode are disposed on a piezoelectric element; A cold cathode fluorescent lamp, Wherein the balanced output is taken out at one end by oscillating the piezoelectric transformer in the longitudinal direction, and the cold-cathode fluorescent lamp is connected to the balanced output. A liquid crystal display device comprising backlight means using a cold cathode fluorescent lamp using a piezoelectric transformer according to any one of claims 1 to 9.